# A Series of Trigonal Arylimido Iron Complexes and the Influence of Oxidation State and Steric Demand on Reactivity

## TL;DR

This paper explores how different aryl azides react with iron complexes, showing how steric effects and oxidation states influence reactivity and product formation.

## Contribution

The study reveals new insights into the reactivity of trigonal arylimido iron complexes influenced by oxidation state and steric demand.

## Key findings

- Trigonal anionic iron(II) imidyl complexes with long Fe–N bonds were synthesized.
- Steric demand affects the formation of tetrazenido complexes and C–H amination reactions.
- Computational analysis shows isoenergetic electronic states for different oxidation forms.

## Abstract

We describe the reaction between the linear iron­(I/II)
silylamides
[FeL2]0,– (L = N­{Dipp}­SiMe3) and aryl azides N3R with different steric demand (R
= Ph, 2-Me-C6H4 (Tol), 2,4-Me2-C6H3 (Xyl), 2,6-
i
Pr2-C6H3 (Dipp), 2,4,6-
i
Pr3-C6H2 (Tripp)). Obtained
trigonal anionic high-spin iron­(II) imidyl complexes exhibit long
Fe–N bonds of approximately 1.76 Å. In case of the largest
substituent (R = Tripp) a slow SiMe3-shift from the ancillary
ligand to the imido nitrogen is observed. In contrast, for the smallest
azide (PhN3) the tetrazenido complex [Fe­(η2-κN:1 κN4-N4Ph2)­L2] is obtained. Isolable imido complexes react nucleophilic
toward benzaldehyde and mesityl isocyanate under cycloaddition to
metallacycles. In case of the neutral precursor [FeL2]
imido iron species were only obtained for R = Tol or Xyl, with Fe–N
bonds of approximately 1.74 Å. Based on computational analysis
these compounds exhibit isoenergetic quintet and triplet states with
shared electronic structures of an iron­(IV) imide, iron­(III) imidyl
and iron­(II) nitrene. For the smallest aromatic azide PhN3, the reaction with FeL2 results directly in C–H
amination of the ancillary ligands. For sterically more encumbered
neutral imido complexes, intramolecular C–H amination requires
heating or irradiation. The observed absence for intramolecular C–H
amination of anionic imido complexes is computationally rationalized.